This invention relates to a dishwasher employing a float device for accurate liquid fill control.
Most automatic dishwashers presently commercially available use timer means and a flow-controlled inlet or constant flow type water valve to meter the desired amount of liquid into the wash chamber. It is well known that due to manufacturing variations, timer inaccuracies and deterioration of the flow controlled inlet valve over time, this approach results in inaccurate fills. To insure against an insufficient fill using this approach, the nominal fill setting is intentionally higher than necessary. This intentional overfill results in satisfactory washability performance but at a cost of greater water and energy usage than is necessary. One means of reducing water usage in a dishwasher is to provide an accurate fill control means which eliminates the need for intentionally overfilling.
The use of float devices in dishwashers is well known in the art primarily for flood control. In this role the float is typically placed in a corner of the wash chamber remote from the sump. This arrangement too provides an inherently inaccurate level control. Two major contributing factors are the placement of the device at a location relatively remote from the center of the machine which makes the liquid level sensing very sensitive to machine levelling, and the relatively large surface area of the pool requiring a relatively large change in liquid volume to make a relatively small change in liquid level. Since accuracy in a flood control device is not essential, this arrangement works satisfactorily for that purpose. However, for the precise control of liquid fill required to enable minimum water usage, such an arrangement is clearly not satisfactory.
It is desirable therefore to provide a dishwasher which provides a simple, reliable and inexpensive arrangement for accurately controlling the amount of liquid used in the machine with a view to minimizing water usage and associated energy consumption.
Thus, it is one object of the present invention to provide a dishwasher with an improved liquid fill level control arrangement.
It is another object of this invention to provide such a dishwasher in which the liquid level control arrangement accurately senses the level of liquid in the wash chamber.
It is yet another object of this invention to provide such a dishwasher in which the liquid fill level control arrangement is relatively insensitive to non-level mounting of the dishwasher.
It is yet another object of this invention to provide such a dishwasher in which the liquid fill level control arrangement is not vulnerable to nuisance tripping.
It is yet another object of this invention to provide such a dishwasher in which the liquid fill level control arrangement includes a float device for accurately sensing the liquid level in the wash chamber.
It is yet another object of the present invention to provide such a dishwasher in which the liquid level control arrangement includes a float device which is capable of accurately terminating fill when the quantity of liquid provided to the wash chamber only slightly exceeds the quantity necessary to maintain the pump in its primed operating condition.